The present invention relates to a swivel which is used to connect a conduit to a string of coiled tubing which is wound upon a reel. More particularly, the invention relates to such a swivel which comprises a mandrel that is rotatably connected to the swivel body with a separate bearing assembly.
Coiled tubing swivels are used in, among other applications, the drilling, cementing and stimulation of oil and gas wells to provide for fluid communication between a service conduit and a coiled tubing string that extends into the well as the coiled tubing string is wound upon or unwound from a reel. Prior art coiled tubing swivels typically include a tubular mandrel which is rotatably received within a cylindrical receptacle that is formed in a swivel body. The swivel body comprises an internal flow path which extends between the receptacle and a port that communicates with the exterior of the swivel body. The coiled tubing string is connected to either the mandrel or the port, and the service conduit is connected to the other of the mandrel or the port. In this manner, fluid communication is established between the coiled tubing string and the service conduit through the swivel.
Prior art coiled tubing swivels also include a conventional swivel assembly to permit the mandrel to rotate relative to the swivel body when the coiled tubing is being wound onto or unwound from the reel. This conventional swivel assembly typically comprises a standard thrust bearing and a relatively complex journal bearing which are designed to withstand the side and bending loads that are imparted on the mandrel. The journal bearing usually includes a number of coaxial bearing races which are defined by matching annular grooves that are formed in the receptacle and on the outer diameter of the mandrel. Once the mandrel is positioned in the receptacle, a plurality of balls are inserted into the bearing races to rotatably secure the mandrel to the swivel body.
The coiled tubing swivel must be capable of containing common service and production fluids at significant pressures and flow rates. Thus, the journal bearing must be made of a material that is sufficiently hard to meet the anticipated bearing load capacity. In addition, the mandrel and the swivel body must be made of materials that will not erode or corrode in the presence of the service fluids which will be conveyed through the swivel. However, materials which are compatible with the service fluids are typically not sufficiently hard for bearing races. Thus, a compromise is often reached by making the mandrel and the swivel body larger than would normally be required in order to increase the amount of material in the areas of the bearing races to ensure that the races will not fail. However, this adds size and weight to the swivel.
The present invention addresses these and other disadvantages in the prior art by providing a coiled tubing swivel for rotatably connecting a first conduit to a second conduit, one of which comprises a string of coiled tubing which is wound upon a reel. The swivel comprises a swivel body which includes a cylindrical receptacle and a flowpath that extends between the receptacle and a port which communicates with the first conduit. The swivel also comprises a tubular mandrel which includes a first end that is received within the receptacle, a second end that communicates with the second conduit, a longitudinal hole that extends between the first and second ends, an outer diameter surface and a flange that extends radially outwardly from the outer diameter surface generally proximate the first end. The swivel further comprises a bearing assembly which is positioned between the receptacle and the mandrel and which includes a central axis, a cylindrical outer sleeve that comprises an inner surface and a number of annular inner grooves which are formed on the inner surface coaxially with the central axis, a cylindrical inner sleeve that comprises an outer surface and a number of annular outer grooves which are formed on the outer surface coaxially with the central axis, wherein the outer grooves align with respective inner grooves to define a number of bearing races, and a plurality of balls that are disposed in the bearing races to rotatably secure the inner sleeve to the outer sleeve. The swivel also includes a seal for sealing the bearing assembly from the flowpath in the swivel body, and a retainer for retaining the bearing assembly within the receptacle. Furthermore, the flange is positioned between the bearing assembly and the swivel body to thereby secure the mandrel within the receptacle.
In a preferred embodiment of the invention, each bearing race comprises a diameter which is smaller than the diameter of the adjacent bearing race which is closer to the first end of the mandrel. In a more preferred embodiment of the invention, the diameter of each bearing race is selected such that each bearing race will hold one less ball than the adjacent bearing race which is closer to the first end of the mandrel.
Thus, the present invention provides a swivel which comprises a separate bearing assembly that is isolated from the fluid in the flowpath. Consequently, the bearing assembly can be made of a material which is not compatible with the fluid. In addition, the bearing races are preferably stepped, with the diameter of each bearing race being smaller than the diameter of each adjacent bearing race which is closer to the first end of the mandrel. In this manner, should the balls or the bearing races fail, the inner and outer sleeves will engage and prevent the mandrel from separating from the swivel body.
These and other objects and advantages of the present invention will be made more apparent from the following detailed description, with reference to the accompanying drawings.